Minecraft v1.16.4
Forge v35.1.13
Double Slabs v3.4.10

If the Cryptic and Green Campfires from Biomes You'll Go and placed as a double slab, it becomes a Soul Campfire. Then I got a server crash when I broke the campfire while it was cooking Assorted Seeds from the Terraqueous mod.
Crash Report

Hi there! Sorry for the delay in fixing this, I believe this is now fixed in the latest version :)